[ubuntu-cloud] Greater than 1TiB boot disks for the Cloud Image

[Scott Moser]

On Fri, 25 Jul 2014, Patrick Devine wrote:

> Hey peeps,
>
> I ran into an interesting problem yesterday with regards to the cloud
> image.  The image contains a single ext4 partition across an MSDOS
> partition table, which I believe is done to make it expedient to
> resize the partition; it's simple to add space to the image and extend
> the the single partition to different instance sizes.
>
> There ends up being two problems, however.  Since it's partitioned
> with MSDOS, the total size of the disk is limited to 2 TiB.  This is
> annoying, but if you're OK with the limitation it will work out of the
> box with OpenStack and KVM.  That is, it will work until a new grub

Right, there is not much we can do at this point about that limitation.
As you pointed out, we do make the uefi images available, and given
appropriate kvm invocation, they should load properly.  growpart (from
cloud-utils) should successfully be able to make them grow to > 2TB.

> package is released.  Grub has a limitation that it can only read
> partitions which are less than 1TiB in size, so if you've resized your
> instance flavour to larger than 1 TiB, you're going to be in trouble.

I talked with grub maintainer Colin Watson and he did not seem to know
about such a limitation.  Do you have a link to such ?

> Everything will work fine initially because Grub gets installed
> initially as part of image creation when the partition size is small.
> When it gets _re-installed_ however (as was the case yesterday when a
> new grub-pc package was released), things will blow up leaving your
> image in a broken state.

I've filed this as bug 1349538 and taken the liberty of subscribing you.
  https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1349538

> I haven't tried the uefi image as I'm not certain whether or not it
> will have issues with KVM.  My guess is that it would at least have a
> GPT partition table, but I don't know if it still suffers from the
> single partition problem which chokes up Grub.
>
> Is there any documentation on the cloud images?  The Community Help
> Page does not mention any limitations, and doesn't even explain how to
> import the image into OpenStack.  It would be nice to know what the

Manually, as you can find in the openstack doc, this is:
  http://docs.openstack.org/user-guide/content/cli_manage_images.html
  glance image-create --name centos63-image --disk-format=qcow2 \
    --container-format=bare --is-public=True --file=your.img

For automated use cases, we provide machine formated data at
  http://cloud-images.ubuntu.com/releases/streams/v1/
That is in 'simplestreams' format, which can be read and used by the
simplestreams package/library.  There is a full example of how to "sync"
images from cloud-images.ubuntu.com into your local glance at:
  http://bazaar.launchpad.net/~smoser/simplestreams/example-sync/view/head:/README

That also creates simplestreams data and uploads it to swift.  Then, if
you know your swift url.  Then, a tool (sstream-query) can be used to
query that data and get the image id of the latest ubuntu image.  Note,
this is what juju reads, and is available for public clouds from that same
streams/v1/ link above.

There is some more information about simplestreams in a talk I did for
UDS.  See https://github.com/smoser/talk-simplestreams .

> limitations are up front so that when you are using them in a
> production environment they don't end up biting you.

Agreed, better documentation would be useful.